This invention relates generally to medical imaging systems, and more particularly, to methods and systems for generating purely T1-weighted images using data from two or more acquisitions.
Magnetic Resonance Imaging (MRI) generates an image based on a plurality of properties specific to a material of an object being imaged. One of the properties is a longitudinal relaxation time T1 and another one of the properties is a transverse relaxation time T2. Known imaging methods generate images by applying a sequence of Radio Frequency (RF) pulses to the object. This sequence is repeated periodically after a time interval TR. The signal produced by the object after applying RF pulses depends on the material of the object and the T1 of that material. MRI employs the property of different T1 relaxation rates for the material of the object to obtain contrast within the image. The image obtained by emphasizing T1 and de-emphasizing T2 of the material is referred to as a T1-weighted image.
The known methods for obtaining the T1-weighted image make use of an inversion or saturation recovery techniques. The inversion recovery technique utilizes a long repetition time and thus results in a long scan time. Saturation recovery techniques may utilize short values of TR. However, short values of TR produce low intensity signals from the object, such as a fetal brain, that have long T1 values. The low signals result in a poor signal-to-noise ratio (SNR). Further, long scans are not useful for the fetal brain because of motion of the fetal brain.
Partial pressure (pO2) of oxygen measurements for fluids such as cerebrospinal fluid, amniotic fluid and urine may be a useful diagnostic tool for a variety of diseases. The pO2 measurements are currently obtained by invasive procedures. However, the invasive procedures are prone to movement of the object and contamination from the environment in which the invasive procedures are performed. A relationship between the pO2 of a fluid and the T1 of that fluid is known to exist. However, obtaining measurements of fluid T1 in order to estimate pO2 has not previously been demonstrated in vivo.